nuclear force (or interaction of the nucleons or the remaining strong force ) is the force that works between protons and atomic neutrons. Neutrons and protons, both nucleons, are influenced by almost identical nuclear forces. Because protons have a charge of 1 e , protons have electric forces that tend to push them apart, but at close range the pulling nuclear force is strong enough to overcome the electromagnetic force. Nuclear forces bind nucleons to atomic nuclei.
The nuclear force is very attractive between nucleons at a distance of about 1 femtometre (fm, or 1.0 ÃÆ'â € "10 -15 meter), but rapidly decreases to insignificant at a distance above about 2.5 f fm. At a distance less than 0.7 fm, the nuclear force becomes disgusting. This disgusting component is responsible for the physical size of the nucleus, because the nucleons can not come closer than the allowable force. By comparison, the size of atoms, measured in angstroms (ÃÆ'..., or 1.0 ÃÆ'â € "10 -10 m), are five larger magnitude orders. Its nuclear force is not simple, because it depends on the spin of nucleons, has a tensor component, and may depend on the relative momentum of the nucleons. A strong nuclear force is one of the fundamental forces of nature.
The nuclear force plays an important role in storing the energy used in nuclear power and nuclear weapons. Work (energy) is required to carry a shared proton against their electrical repulsion. This energy is stored when the protons and neutrons are bonded together by the nuclear force to form the nucleus. The nucleus of the nucleus is less than the total mass of individual protons and neutrons. The mass difference is known as the mass defect, which can be expressed as the energy equivalent. Energy is released when heavy nuclei break into two or more lighter nuclei. This energy is the electromagnetic potential energy that is released when the nuclear force no longer holds the charged nuclear fragments together.
The quantitative description of the nuclear force depends on partially empirical equations. These equations model the potential, potential, or potential of international energy. (In general, the forces in a particle system can be simplified by modeling the potential energy of the system: the negative gradient of a potential is equal to the vector force.) The constant for the equation is phenomenologically determined by adjusting the equations for the experimental data. The potential of internucleon tries to describe the interaction properties of nucleons. Once determined, any given potential can be used, for example, the Schrödinger equation to determine the quantum mechanical properties of the nucleon system.
The discovery of neutrons in 1932 reveals that atomic nuclei are made of protons and neutrons, which are united by interesting forces. In 1935, the nuclear force was conceived to be transmitted by particles called mesons. This theoretical development includes a description of Yukawa's potential, an early example of a nuclear potential. Meson, predicted by theory, was discovered experimentally in 1947. In the 1970s, quark models have been developed, where mesons and nucleons are seen as composed of quarks and gluons. With this new model, the nuclear force, which results from the exchange of mesons between neighboring nucleons, is a residual effect of a strong force.
Video Nuclear force
Description
While the nuclear force is usually associated with nucleons, more commonly this force is felt between hadrons, or particles composed of quarks. At the small separation between nucleons (less than ~ 0.7 fm between their centers, depending on the spin alignment) the forces become disgusting, which makes the nucleons at a certain average separation, even if they have different types. This expulsion arises from Pauli exclusion forces for identical nucleons (such as two neutrons or two protons). The Pauli exclusion force also occurs between quarks of the same type in nucleons, when different nucleons (protons and neutrons, for example).
Field Strength
At a distance greater than 0.7 Â ° fm the force becomes attractive between the spin-aligned nucleons, being maximal at a central center distance of about 0.9 fm. Beyond this distance, the force falls exponentially, up to a distance of 2.0 fm, the force can be ignored. Nucleon has a radius of about 0.8 degrees fm.
At short distances (less than 1.7 fm or more), the attractive nuclear force is stronger than the disgusting Coulomb force between protons; thus overcoming the proton rejection within the nucleus. However, the Coulomb force between protons has a much larger range because it varies as the inverse square of charge separation, and Coulomb repulsion becomes the only significant force between protons when their separation exceeds about 2 to 2.5 fm.
The nuclear force has components that depend on the spin. This force is stronger for particles with their spins aligned than for those with their anti-spin spins. If two particles are alike, like two neutrons or two protons, force is insufficient to bind particles, since the rotation vectors of two particles of the same type must point in the opposite direction when the particles are close together and (save for spin) in the same quantum state. The requirements for this fermion are derived from the Pauli exclusion principle. For fermion particles of various types, such as protons and neutrons, the particles can be adjacent to each other and have rotated parallel without violating the Pauli exclusion principle, and the nuclear force can bind it (in this case, to deuterons), since the nuclear force is much stronger for particles spin-aligned. But if the spins of the particles are anti-aligned, the nuclear force is too weak to bind them, though they have different types.
The nuclear force also has a tensor component that depends on the interaction between rotating nucleons and the momentum of the nucleon angle, which causes the deformation of a simple round shape.
Nuclear Binding
Dismantling the nucleus into protons and unbound neutrons requires work against the nuclear force. Instead, energy is released when the nucleus is made from free nucleons or other nuclei: nuclear binding energy. Because of the mass-energy equivalence (ie the famous formula Einstein E = mc 2 ), releasing this energy causes the mass of the nucleus lower than the total mass of individual nucleons, leading to the so-called "mass defects".
The nuclear force hardly depends on whether the nucleon is a neutron or proton. This property is called self-reliance . The force depends on whether the parallel or antiparallel nucleon spins, because it has a non-central component or tensor . This section of force does not preserve the orbital angular momentum, which under the action of central force is preserved.
The symmetry that produces the strong force, proposed by Werner Heisenberg, is that protons and neutrons are identical in all things, apart from their cargo. This is not entirely true, because neutrons are slightly heavier, but this is an approximate symmetry. Therefore, protons and neutrons are seen as the same particle, but with different isospin quantum numbers. Strong forces are invariant under SU (2) transformations, as do particles with intrinsic twists. Isospin and related intrinsic spins in this symmetry group SU (2). There is only a strong attraction when the total isospin is 0, which is confirmed by the experiment.
Our understanding of the nuclear force is obtained by spreading experiment and binding energy from the light core.
Nuclear forces occur with the exchange of virtual light mesons, such as virtual pawns, as well as two types of virtual mesons with spin (meson vector), rho meson and omega mesons. Records of meson vectors for nuclear spin-force dependence in this "meson virtual" image.
The nuclear force is different from what has historically been known as the weak nuclear force. Weak interaction is one of four fundamental interactions, and plays a role in processes such as beta decay. The weak force does not play a role in the interaction of the nucleons, although it is responsible for the decay of neutrons into protons and vice versa.
Maps Nuclear force
History
The nuclear army has been at the heart of nuclear physics since it was born in 1932 with the invention of neutrons by James Chadwick. The traditional aim of nuclear physics is to understand the nature of atomic nuclei in terms of 'naked' interactions between nucleon pairs, or nucleons (NN forces).
Within months of the discovery of neutrons, Werner Heisenberg and Dmitri Ivanenko had proposed proton-neutron models for the nucleus. Heisenberg approached the description of protons and neutrons in the nucleus through quantum mechanics, an entirely uncertain approach at the time. The Heisenberg theory for protons and neutrons in the nucleus is "a major step toward understanding the nucleus as a system of quantum mechanics." Heisenberg introduced the first theory of nuclear exchange power that binds nucleons. He considers protons and neutrons to be different quantum states of the same particle, ie, nucleons that are distinguished by their nuclear quantum isospin number values.
One of the earliest models for the nucleus was the liquid drop model developed in the 1930s. One of the properties of nuclei is that the mean binding energy per nucleon is almost the same for all stable nuclei, which is similar to a drop of liquid. The liquid drop model treats the nucleus as a drop of nuclear liquid that can not be compacted, with nucleons behaving like molecules in liquids. The model was first proposed by George Gamow and later developed by Niels Bohr, Werner Heisenberg and Carl Friedrich von WeizsÃÆ'¤cker. This rough model does not explain all the core properties, but it does explain the round shape of most of the atomic nuclei. This model also provides good predictions for nuclear nuclear energy from nuclei.
In 1934, Hideki Yukawa made the earliest attempt to explain the nature of nuclear force. According to his theory, the big boson (meson) mediates the interaction between the two nucleons. Although, in the light of quantum chromodynamics (QCD), the meson theory is no longer considered a fundamental, meson exchange concept (where hadron is treated as a basic particle) continues to represent the best working model for quantitative NN
where g is a constant large scale, that is, the potential amplitude, is the mass of Yukawa particles, r is the radial distance to the particles. Monotonic potential increases, implying that style is always attractive. The constants are empirically determined. The potential of Yukawa depends only on the distance between the particles, r , then it models the central power.
Throughout the 1930s, a group at Columbia University led by I. I. Rabi developed a magnetic resonance technique to determine the atomic magnetic moment. This measurement led to the discovery in 1939 that deuterons also have electric quadrupole moment. This power of deuterons has disrupted measurements by the Rabi group. Deuteron, made up of protons and neutrons, is one of the simplest nuclear systems. This discovery means that the physical form of the deuteron is not symmetrical, which provides valuable insight into the nature of the nuclear force that binds the nucleons. In particular, the results show that the nuclear force is not a central power, but has a tensor character. Hans Bethe identified the discovery of the deuteron quadrupole moment as one of the important events during the formative years of nuclear physics.
Historically, the task of describing nuclear forces is phenomenologically strong. The first semi-empirical quantitative model came in the mid-1950s, such as the Woods-Saxon potential (1954). There was substantial progress in experiments and theories associated with nuclear forces in the 1960s and 1970s. One of the influential models was Reid's potential (1968).
In recent years, researchers have concentrated on the subtleties of the nuclear force, such as its load dependence, precise values ​​of constant NN merging, improved phase shift analysis, high precision NN data, high precision NN potential, NN scattered at medium and high energy, and efforts to lower the nuclear force of QCD.
Nuclear force as the rest of strong force
The nuclear force is a residual effect of stronger, more fundamental forces, or strong interactions. Strong interactions are the exciting forces that bind to the fundamental particles called quarks together to form the nucleons (protons and neutrons) themselves. This stronger force is mediated by particles called gluon. Gluons hold the quark together with a force like an electric charge, but a much larger force. Quarks, gluons and their dynamics are largely confined to nucleons, but the residual influence extends slightly beyond the limits of nucleons to produce nuclear forces.
The nuclear force that arises between nucleons is analogous to the chemical forces between neutral or molecular atoms called London powers. The forces between the atoms are much weaker than the attractive electric forces that hold the atoms themselves together (ie, which bind the electrons to the nucleus), and their range between the atoms is shorter, because they arising from the small separation of charge inside the neutral atom. Similarly, although nucleons are made of quarks in combinations that cancel most of the strength of the gluon (they are "color-neutral"), some quark and gluon combinations remain leaky from the nucleons, in the form of short-range nuclear force fields extending from one nucleon to the other nearby nucleons. This nuclear power is very weak compared to the direct gluon force ("color strength" or strong force) inside the nucleons, and nuclear power only extends over several nuclear diameters, falling exponentially with distance. Nevertheless, they are strong enough to bind neutrons and protons at short distances, and overcome electrical repulsions between protons in the nucleus.
Sometimes, the nuclear force is called the strong force of rest , in contrast to the strong interactions emerging from QCD. This phrase emerged during the 1970s when QCD was being formed. Prior to that time, strong nuclear forces were referring to the inter-nucleon potential. After verifying the quark model, strong interaction has become a mean QCD.
Nuclear-nucleon potential
Two-nucleon systems such as deuterons, deuterium nuclei, and proton-protons or neutron-proton scattering are ideal for studying the power of NN . Such a system can be described by connecting potential (like the potential of Yukawa) to the nucleons and using the potential in the Schrödinger equation. The potential form is phenomenologically derived (based on measurement), although for long-term interactions, meson exchange theory helps build potential. The potential parameters are determined appropriately to the experimental data such as deuteron binding energy or NN the elastic scattering cross section (or, equivalent in this context, is called NN phase shift).
The most widely used NN potentials are Paris, potential Arg18 AV18, CD-Bonn potential and Nijmegen potential.
A newer approach is to develop effective field theories for a consistent description of the nucleons and the strength of the three nucleons. Quantum hadrodynamics is an effective field theory of nuclear force, proportional to QCD for color interaction and QED for electromagnetic interactions. In addition, the chiral symmetry split can be analyzed in terms of effective field theory (called chiral perturbation theory) which allows the perturbative calculation of the interaction between nucleons with pawns as exchange particles.
From nucleon to core
The ultimate goal of nuclear physics is to describe all nuclear interactions of the basic interactions between nucleons. This is called microscopic or ab initio the nuclear physics approach. There are two major hurdles to overcome before this dream can come true:
- Calculations in many-body systems are difficult and require advanced calculation techniques.
- There is evidence that the power of three nucleons (and possibly higher multi-particle interactions) plays an important role. This means that the potential of three nucleons should be incorporated into the model.
This is an active research area with ongoing progress in computational techniques leading to the first principles of better calculation of nuclear shell structures. Potential two and three nucleons have been implemented for nuclides up to A Ã, = Ã, 12.
Nuclear potential
A successful way of describing nuclear interaction is to build a potential for the entire core rather than considering all its nucleon components. This is called the macroscopic approach. For example, the neutron scattering of the nucleus can be explained by considering the plane wave in the core potential, consisting of real parts and imaginary parts. These models are often called optical models because they resemble light cases scattered by frosted glass spheres.
Nuclear potentials can be localized or global : local potentials are limited to narrow energy ranges and/or narrow nuclear mass ranges, while global potentials, which have more parameters and are usually less accurate, is a function of energy and nuclear mass and hence can be used in a wider range of applications.
See also
- Strong interactions
- Standard Model
References
Bibliography
- Gerald Edward Brown and A. D. Jackson, Nucleon-Nucleic Interactions , (1976) North-Holland Publishing, Amsterdam ISBN 0-7204-0335-9
- R. Machleidt and I. Slaus, "Nucleon-nucleon interactions", J. Phys. G 27 (2001) R69 (topical review) .
- E.A. Nersesov, Fundamentals of atomic and nuclear physics , (1990), Mir Publisher, Moscow, ISBN 5-06-001249-2
- P. NavrÃÆ'¡til and W.E. Ormand, "Ab initio shell model with the power of three original nucleons for p-shell core", Phys. Pdt. C 68 , 034305 (2003).
Further reading
- Nuclear Force Ruprecht Machleidt, Scholarpedia, 9 (1): 30710. doi: 10.4249/scholarpedia.30710
Source of the article : Wikipedia
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